It is a common practice in an optical network to introduce a signal tracking mechanism, which would allow the distinguishing and supervising of individual wavelength channels along the optical path. Commonly the tracking mechanism is implemented by modulation of a wavelength channel with a low frequency dither tone, which is unique to the transmitted channel and remains unchanged as the channel travels through the network. This approach has been described in several articles, patents and patent applications, some of which are listed below:    1. U.S. Pat. No. 5,513,029 to Kim Roberts et al;    2. Canadian Patent Application Serial No. 2,288,463 to James Harley;    3. A publication by Fred Heismann, Mohammad T. Fatehi, Steven K. Korotky and John J. Veselka entitled “Signal Tracking and Performance Monitoring in Multi-Wavelength Optical Networks”, WeB.2.2., 22nd European Conference on Optical Communications, ECOC '96, Oslo, pp. 3.47–3.50; and    4. A publication by G. R. Hill, P. J. Chidgey, F. Kaufhold, et al, “A Transport Network Layer Based on Optical Network Elements”, Journal of Lightwave Technology, Vol. 11, No. 5/6, May/June 1993, pp. 667–679.
Although the approaches described in the cited prior art provide useful information and identification of different optical signals (wavelengths channels) in a network, their origin and power levels, this information alone is limited and not sufficient for the efficient monitoring of the performance of the optical network.
Accordingly, there is a need in industry for the development of improved methods and systems for monitoring performance of optical networks, which would capture more information about the network and therefore would be more accurate and efficient.